On 05/13/2016 04:38 PM, Mel Beckman wrote:
But another key consideration beyond accuracy is the reliability of a server's
GPS constellation view. If you can lose GPS sync for an hour or more (not
uncommon in terrain-locked locations), the NTP time will go free-running and
could drift quite a bit. You need an OCXO to minimize that drift to acceptable
levels.
While this is drifting a bit off-topic for NANOG (and drifting into the
topic range for time-n...@febo.com), I'll just add one more thing to
this. The Hold time (when the oscillator is free-running) is a very
important consideration, especially, as you say, when terrain is an
issue. For us it is even more important, as the 10MHz output from the
timing rack is used as a site-wide frequency standard. Of course, you
never discipline a cesium PRS, but the rubidium secondary is disciplined
by circuitry in the SSU2000.
Back in the days of common backbone delivery over SONET discussion of
cesium standards would have been on-topic, as some SONET gear (Nortel
Optera for instance) needs a master clock; especially if you were
delivering channelized circuits or interfacing with customers and telcos
with DS3 or even DS1 circuits or DS0 fractions within them. Ethernet is
far more forgiving.
